SUMMER TRAINING REPORT

ON

BUILDING CONSTRUCTION

Submitted by Submitted to

Civil 3rd year (Civil Department)

                 

 

ACKNOWLEDGEMENT

Training is one of the most important aspects for an engineering student’s career. It’s basically to strengthen the theoretical concepts and to get them aware of the new working technology. Through this training a student get’s acquainted with latest technology and recent developments.

I am extremely thankful to Mr.___(project Manager) for providing and to work on my project And also; I convey my sincere thanks to all the employees of U.P.Project corporation ltd. Their love and guidance was omnipotent and incompatible throughout the training period.

_______IIIrd YearCivil Engg.

   Content INTRODUCTION

BUILDING MATERIAL

EFFECT OF AGGREGATE PROPERTIES ON CEMENT CONCRETE 

REINFORCEMENT CEMENT CONCRETE AND DESIGN 

PHILOSOPHY

COMMAN TEST ON FRESH CONCRETE 

INDEX

                                              

INTRODUCTION

ABOUT COMPANY

   U. P. PROJECTS CORPORATION LTD. is a U. P. Govt. undertaking entrusted with construction of Infrastructure Projects e.g. Residential, Non-residential buildings including Hospitals, Colleges, Offices etc, Dams, Canals and different types of Hydraulic Structures, Roads and works related to Rural Development. The Corporation is carrying out projects in the State of Uttar Pradesh as well as other states of the country.           In year 1999 U.P. Govt. declared the corporation as CONSTRUCTION AGENCY vide G.O. No. 1434/99-27-Irrigation-5-36 Tw. Dt. 14-7-99 for construction of shallow and deep tubewells, hydrological structure such as Barrage, aquaduct, syphon, pump house, drainage, lining of canals, reservoir, underground and over head water tanks and  distribution systems etc. In the year 2001 Govt. of U.P. again recognized it as Construction agency for construction of buildings wide letter no    U. P. PROJECTS CORPORATION LTD. is a U.P. Govt. undertaking entrusted with construction of Infrastructure Projects e.g. Residential, Non-residential buildings including Hospitals, Colleges, Offices etc, Dams, Canals and different types of Hydraulic Structures, Roads and works related to Rural 

Development. 

      In year 1999 U.P. Govt. declared the corporation as CONSTRUCTION AGENCY vide G. O. No. 1434/99-27-Irrigation-5-36 Tw. Dt. 14-7-99 for construction of shallow and deep tubewells, hydrological structure such as Barrage, aquaduct, syphon, pump house, drainage, lining of canals, reservoir, underground and over head water tanks and  distribution systems etc. In the year 2001 Govt. of U.P. again recognized it as Construction agency for construction of buildings wide letter no.   E-8-667/10/06-89/2004 Dt. 6 June 2006.

     As a result of diversification the turnover of the corporation substantially increased from Rs. 640.45 lacs in 1999 to    Rs. 21,229.47 lacs in 2005-2006. 

     The  Corporation aims at procuring and executing jobs of residential and non residential buildings, roads. Hydraulic structures, Industrial buildings, fabrication & erection of plant and machinery, drilling of deep public and private tubewells, laying of water distribution pipe lines and other Civil and Mechanical  works. This Corporation also take-up works on TRUNKEY BASIS . While executing various jobs the corporation strives to eliminate big contractors/middle men by employing the concept of departmental construction. This ensures ECONOMY, QUALITY , AND SPEED in construction activities. ABOUT PROJECT

The building is defined as any structure what so ever

purpose and of whatsoever materials constructed and ever

part thereof whether used as human habitation or not. For

this practical training.

I reported at Balrampur district at Construction of District hospital ai Balrampur in response to Mr. G.K.Singh(Project Manager) dated 10.06.2012. The site incharge Mr. R.M.Maurya meet me at the site and gives me brief introduction of this project as under.

This project has the following features:Location : Utraula raod ,BalrampurEarthquake zone : 3Construction company : U.P.Project corporationStructural consulant : Rajiv Kumar & AssociatesCost of the Project : 20.6 carore rupees

The building is fully air-conditioned. It have fire detection system and fire fighting system and escape way in the carious condition. This building is earth quack resistance.Frame strecture is used as earthquake resistant tecnnique.

Some projects of U.P.Project corporation are Ch.Charan Singh Kurar Dam Jhasi,Dr.Avad university Faizabad, Sidicul Pharama city,Drhradun ect.

TECHNICAL REPORT

1 Foundation concrete: Design mix concrete M-252 Foundation: R.C.C. Raft foundation

having slab thickness700 mm

3 Wall: (a) Basement outer wall ofR.C.C. Retaining typein cement concrete M-25

(b) Ground floor & first floorother wall of R.C.C. incement concrete M-25 &Brick masonry in cementmortar 1:6 230 mmthick with bricks of classdesignation 100

4 Structure The complete structure isof RCC frame structure inM-25 concrete.

5 Sanitary & watersupply fitting (a) Conclealed G.I. fitting in

side building with brassfitting.

(b) Out side fitting are ofopen type.

6 Other specifications (a) Expansion &Contractionjoint are provided.

(b) bitumen treatment areprovided at the roof.

(c) Plasticizer used: cicoplasticizer tape Crete P-151 polymer mix in the

concrete at the rate of 1%of weight of cement used.

7 Estimate Cost The estimate cost of abovebuilding comes to Rs. 25.6crores .

BUILDING MATERIAL

A building structure is composed of different types of the material these materials are either called as building material. The material use in the building on basis of the avaibility and cost. For construct a building the essential building material are as follow:

Cement

The cement often called the magic power is a fine ground material consisting of compound of lime ,silica alumina and iron. When mixed with water it forms a paste which hardened and bind the aggregates (sand, gravel, crushed rock, etc) together to form a durable mass called the Concrete. Cement is the binder that holds concrete and mortars together. Which is why it play the most critical role in giving strength and durability to your building. Cement uses for domestic building such as home are basically of three types.

Portland Slag Cement: Portland slag cement(PSC) conforming to IS: 455 A combination of good quality blast furnace slag (from the iron steel industry) with clinker (which makes the OPC) and gypsum.

8

Portland Pozzolana Cement: Portland pozzolanacement (PCC) conforming to IS: 1489 A combination of flyash (from thermal power plant) with clinker and gypsum. pozzolana cement is prepared by grinding Portland cement clinker with pozzolana. This type of cement is largely used in marine structure.

Ordinary Portland Cement: Ordinary Portlandcement (OPC) 33 grade conforming to IS: 269, 43 grade conforming to IS: 8112 and 53 grade conforming to IS: 12269 A combination of clinker and gypsum of good quality. Ordinary Portland cement is manufactured by first burning at a very high temperature the mixture of calcareous (mainly calcium carbonate) and argillaceous (mainly clay) and then grinding the calcined product (i.e. clinker) with small amount of gypsum in to a fine power known as ordinary Portland cement.

Good quality cement has the following features:

· Reduced water requirement · Improve Workability · Less permissible to moisture · Improved resistance to acid and chlorides · Reduced heat of hydration · Easier to finish · Reduced shrinkage

· Reduced leaching problems because it is low as free lime.

Sand

These are cohesion less aggregates of either, rounded sub rounded, angular, sub angular or flat fragments of more or less unaltered rock of minerals consisting of 90% of particles of size greater than 0.06 mm and less than 2 mm. Alternatively, these are coarse grained cohesion less particles of silica derived from the disintegration of rock. These are of three types:

Coarse sand: It is one which contains 90% of particles of size greater than 0.6 mm and less than 2 mm.

Medium sand: It is one, which contains 90& of particles of particles size greater than 0.2 mm and less than 0.6 mm.

Fine sand: It is one, which contains 90% of particles of size greater than 0.06 mm and less than 0.2 mm.

Proper selection of sand is critical in the durability and performance of concrete mixture. It should be:

· Clear, angular and hard · Free from clay, mica and soft, flaky material · Graded, which means it should be a mix of fine,

medium and coarse sand · Fee from contaminates like sea salt · Consistent in moisture (water) content which should

not exceed 7%. When mixing concrete the moisture content must be taken in to consideration.

The price of sand includes three or four components-base cost, transportation, handling and number of intermediaries. Procuring sand in bulk directly from the source will be cheaper. Your neighborhood dealer in this case is likely to be costlier, except when you need smaller quantities.

Building Stone

Building stones are obtained from the rocks occurring in nature. The stones are used in to construct the foundation, super structure and many of the building component. The various stones derived from these types of rocks are as follows:

v Principal stones from igneous rocks: Granite, Basalt and Trap

v Principal stones from sedimentary rocks: Sand stone, Shale, Lime stone

v Principal stones from metamorphic rocks: Quartzite, slate and marble

Properties or requirement of good building stone:A good building stone should posses several

characteristics such as high strength (crushing strength>1000kg/cm²), high durability, sufficient hardness (coefficient of hardness>14), high resistance to wear, good fire resistance, specific gravity more than 2.7, crystalline structure, high impact value (toughness index> 13) low water absorption

(percentage absorption after 24 hour less than 0.6), weather resistance and better appearance.

Bricks

Bricks are distinguished by their base (row) material and size. Standard brunt clay bricks come in the size 10" x 5" x 3". Modular bricks, rarely used because they are not easily available, come in the size 200mm x 100mm x 100mm (including mortar thickness) Fly ash bricks, sometimes also come in modular form.

Conventional bricks have a ‘frog’ (depressed / raised portion) on one of the larger surface bearing the manufacturer’s brand. These also provide a good mechanical key for bonding (lock ability) with mortar. The modular bricks do not have the frog on them. Fly ash bricks exhibit almost similar mechanical properties as brunt clay bricks. Exposed brickwork with precise pointing is possible if the shapes are perfect.

The four board categories of bricks used in construction:

1st class 2nd Class 3rd Class Over bruntBricks Bricks Bricks Bricks

1. Perfect in Not so uniform Much interior AbsolutelySize/shape/ as 1st class to 2nd class out shape ofquality of bricks in shape/ bricks in terms and size,

burning size/quality of of shape/size over burnt,burning and burning fused with

more bricks,with a honeycomb texture

2.Red to Dark red tocherry black in colourred in colour

3.Do not DO not absorbabsorb more more than 25%than 15 to water of own17% of their weight if keptown weight submergedif kept under watersubmerged for one hourfor one hourunder water

Aggregate

‘Aggregates’ is a general term applied to those inert (that chemically inactive) material, which when bounded together by cement, form concrete. Most aggregates used in this country are naturally occurring aggregates such as sand, crushed rock and gravel.

Aggregates for concrete are divided into three categories:

Fine Aggregates: Most of which passes through 4.75 mm I.S. sieve and retained on 150 micron.

Coarse Aggregates: Most of which passes through 63 mm I.S. sieve and retained on 4.75 micron. All in Aggregate: Mixed aggregate, as it

comes from the pit or riverbed. It is some times used for unimportant work without separating into different sizes.

Properties of Natural Aggregates:

The properties should comply with the norms laid down in IS: 38-1970 Specification for C.A. and F.A. from natural sources for concrete. Aggregates should be chemically inert, strong, hard, durable, of limited porosity (water absorption when immersed in water for 24 hours should not be more than 10%.), free from adherent coating, clay lumps, coal and coal residues and should contain no organic or other admixture that may cause corrosion of the reinforcement or impair the strength or durability of the concrete. The shape (rounded, irregular, angular and flaky) and sizes of the aggregates should conform to the strength and workability requirements.

Uses of the Aggregates:1. Naturally occurring crushed stone aggregates can be

used for producing any type of good concrete or R.C.C. for construction purpose.

2. Broken brick aggregates is used to produce plain concrete but not suitable for R.C.C. which is lighter than broken stone aggregate.

3. Air- cooled blast furnace slag, which is a by- product in the process of pig iron, forms a stronger and durable concrete when mixed with sand, and has a high fire resistance.

4. Lightweight aggregate produce low density concrete, which can be used for interior parts of the building where high strength are not desired.

Reinforcement Steel

RCC stands for reinforced cement concrete. To enhance the load carrying capacity of the concrete it is reinforced with steel bars of different diameters provided in an appropriate manner. Such concrete is called reinforced concrete and the bars are called the reinforcement. These bare are provided at various locations to resist the internal forces, which are developed due to the loads acting on the structure.

Reinforcing steel contributes to the tensile strength of the concrete. Concrete has low tensile, but high compressive strength. The tensile deficiency is compensated by reinforcing the concrete mass through insertion of plain or twisted mild steel bars. Both branded and unbranded bars are available. It is wise to buy good brands the names of which are marked on the steel. During construction make sure that steel reinforcement is provided exactly as the engineering design specification.

Precautions: Steel bars/rods should be responsibly clean and free

of rust. Bars that cannot be easily bent manually or

mechanically should be rejected.· Optimum length bars must not be chosen to reduce

wastage in cutting. · To avoid laps, shorter bars must not be accepted · Welded length of the bars should not be accepted

Water

The strength and durability of concrete depends also on the

amount of water mixed with it. Too much or to little water can adversely effect the strength of concrete. After concrete is cast, water is used to cure it so that the temperature is controlled and concrete matures slowly.

It is very important to use clean, potable water in quality concrete production. Brackish or salty water must never be used. Contaminated water will produce concrete mortars with lower durability, erratic set characteristics and inconsistent colour.

THE EFFECTS OF THE AGGREGATE PROPERTIES ON THE CEMENT CONCRETE

Concrete is a mixture of cementious material, aggregate and water. Aggregate is commonly considered inert filler, which accounts for 60 to 80% of the volume and 70 to 85% of the weight of the concrete. Although aggregate is considered inert filler, it is a necessary component that defines the concrete’s thermal and elastic properties and dimensional stability.

Physical and mineralogical properties of aggregate must be known before mixing concrete to obtain a desirable mixture. These properties include shape and texture, size gradation, moisture content, specific gravity, reactivity, soundness, and bulk unit weight. These properties along with water /cementitious material ratiodetermine the strength, workability and durability of the

concrete.

The shape and texture of the aggregate affects the properties of fresh concrete more than hardened concrete. Concrete ids more workable when smooth and rounded aggregate is used instead of rough angular or elongated aggregate. Crushed stone produces much more angular and elongated aggregate, which have a higher surface to volume ratio better bond characteristics but require more cement paste to produce a workable mixture.

The surface texture of the aggregate can be either smooth or rough. A smooth surface can improve workability yet a rougher surface generates a stronger bond between the paste and the aggregate creating a higher strength.

The grading or size distribution of aggregate is an important characteristic because it determines the paste requirement for workable concrete. The required amount of the concrete paste is dependent upon the amount of void space that must be filled and the total surface area that must be covered. When the particles are of uniform size the spacing is the greatest but when a range of sizes is used the void spaces are filled, the less workable the concrete becomes, therefore, a compromise between workability and economy is necessary.

The moisture content of an aggregate is an important factor when developing the proper water/cementitious material ratio.

The density of the aggregate is required in mixture proportioning to establish weight- volume relationships.

REINFORCEMENT CEMENT

CONCRETE

Plain concrete is very strong in compression but its tensile strength is only about 1/10th of the strength in compression. So, the use of the plain concrete is limited to the structure in pure compression. Steel being equally strong in compression and tension, is, there fore, used to reinforce the concrete in a suitable way so that it can be used to build supporting structure where tension also develops. Concrete, thus reinforced is known as “reinforced concrete”.

This combination is made because long steel bars can develops its full strength where it cannot carry equal amount of compressive force due to its buckling which is caused by the slenderness. Thus, the combination of concrete and steel bars has proved to be ideal, as the two material are used to resist the stresses for which they are most suitable.

Properties of the reinforcement cement concrete

1) The concrete develops very good bond with the surface of the steel bars and , there fore the stresses are transferred from one material to the other which cannot resist individually.

2) The steel possesses a high tensile strength, a high modulus of elasticity and same coefficients of expansion and contraction as concrete. Due to equal linear coefficients, no internal stresses are set up within reinforced concrete due to variation in temperature.

3) The coating of cement grout or paste on the surface of the reinforcement protects it from corrosion and at the same time it does not chemically react with the reinforcement.

Advantage of the reinforcement concrete:

1) It is overall economical in ultimate cost. 2) Its monolithic character provides more rigidity to

the structure.

3) It is highly durable and fire resisting. It is not affected by the vermin’s termite’s fungus or such other insects.

4) Well-compacted R.C.C. structure is impermeable to moisture penetration.

5) Care and cost of maintenance of R.C.C. structure are almost negligible.

6) The fluidity of the concrete and flexibility of reinforcement make it to possible to mould the R.C.C. members into variety of shapes desired.

Design philosophy

R.C.C. design of building is being carried out mainly by three methods of design. They are namely: (1) Working stress method (2) Ultimate load method and (3) Limit state method.

The Limit state method is now is vogue in all government design offices and premier private consulting firms. The B.I.S. have published I.S.: 456-2000 incorporating the use of the Limit state method of design. The designer should therefore get well versed with the theory of Limit state method.

Working Stress Method: In this method the design is based on the working load and the criterion for the strength of the structure is its capacity to sustain the loads and forces imposed on it.

Ultimate Load Method: The ultimate load method of design is based on a determination of the load at which a structure fails and a certain factor safety is obtained.

Used over decades, this method is now practically outdated in many advanced countries of the world, because of its inherent limitation

The I.S.: 456-2000 code gives emphasis on Limit State Method, which is modified from of Ultimate Load Method.

Limit State Method is a judicious amalgamation of Working Stress Method and Ultimate Stress Method, removing the drawback of both of the method but retaining their good points. It is also based on sound scientific principles and backed by 25 year of research.

The Limit State Method has proved to have an edge over the Working Stress Method from the economic point of view. Consequently we need no stick to Working Stress Method any more.

Accordingly design circle in P.W.D. is designing the R.C.C. structure as per Limit State Method.

Besides analytical part of the structural design, following factors should also be kept in mind while designing the structure.

a) Strength of structure. b) Durability of structure.

c) Serviceability of structure during construction as well as during design lifetime of structure.

d) Economy in building material and ease of constructions.

e) Economy in centering and formwork. f) Aesthetics of structure

Cement concrete

Cement concrete is a composite material used for construction of various civil engineering structures. It is obtained by mixing the basic ingredients such as cement, fine aggregate (normally sand) and coarse aggregate (normally stone pieces) in required proportions. Water is added in the required measure and the mixture is put into a mechanical mixer to achieve concrete. Concrete is poured into the formwork (mould made up of plywood, steel plates and timber) to get the desired shape. It is then vibrated to achieve proper compaction (uniform denseness). High temperature is generated through chemical reaction in this process. Curing (control of temperature) with water is essential to achieve the desired strength of the concrete.

Concrete gains compressive strength progressively with time. The strength achieved at the end of the 28 days is called the Characteristics Compressive Strength of the concrete and is designed as a Grade. About 60% of this strength is achieved at the end of the 7 days from the date of casting. Concrete continues to gain strength even

beyond 28 days, albeit marginally. The form is subsequently removed. Different compressive strength of the concrete can be achieved by mixing the basic ingredients in different proportions. Being a material moulded at site, the durability of the concrete over a long period of time depends on its mixing, placement, vibration and curing which together contribute to its ‘workmanship’.

Properties of Cement concrete

Strength of concrete:-It should be have high compressive strength. The tensile and shear strengths are generally about 8 to 12 % and 8 to 10 % of their compressive strength respectively.The compressive strength of concrete is effected by several factors such as (a) quality of the material and grading of the aggregates (b) water (c) water cement ratio (d) cement content (e) age of the concrete (f) method of mixing placing compacting and curing

Workability of concreteThe concrete should have sufficient workability. The workability of the concrete indicates the ease with which it can be mixed, placed and compacted. Generally the strength decreases with increases of the workability.

Durability of concreteThe concrete posses a high durability value, as it is not much affected by atmospheric action. On the contrary, with the age, the concrete goes on hardening, thereby increase in the strength. It is this property, which gives this material a distinct place among the building material.

Elasticity of concreteThe concrete is not a truly elastic material and elastic modulus is effect by the strength, age, and moisture content of the concrete and the type of the aggregate used. The concrete undergoes an extra strain in addition to instantaneous strain on application of a load or stress, sufficient time. T his extra strain is called ‘creep of concrete’ and is permanent in character not recovered on the removal of load.

Shrinkage of concreteThe concrete has a tendency to shrink under following conditions:-(a) There is initial shrinkage of cement concrete, which is mainly due to loss of water through forms, absorption by surface of forms. (b) The shrinkage of cement concrete occurs as it is hardened. This tendency of shrinkage on one-hand causes cracks in concrete, while on the other, it grips the reinforcement tightly and hence proper bond between concrete and reinforcement when used in R.C.C. work

Fire resistance of concrete

Concrete is good insulator and has a fairly good fire resistance owing to the presence of pores and also water.

Workability

Workability is the most elusive property of concrete. A concrete is said to be workable if it can be easily mixed,

handled, transported, placed in position and compacted. A workable concrete should not show any segregation Or bleeding.

The segregation is said to occur when the coarse aggregate tries to separate out from the finer material and this result in concentration of coarse aggregate at one place and fine material at another place in the mass concrete. The segregation creates larger voids and reduces the durability and strength both.

The bleeding of concrete is said to occur when excess water comes up at the surface of the concrete. This causes the undesirable small pores through the mass of the concrete.The workability of the concrete effected by many factors: -(a) Shape of the aggregates (b) grading and size of the aggregates (c) ratio and coarse and fine aggregates (d) efficiency of mixing (e) quantity of water and use of any mixture.

For maximum strength, the desired workability of fresh concrete can be attained by the following measure:

(i) The proportion of coarse aggregate may be reduced, because the finer is the grading, the greater will be the workability.

(ii) The proportion of coarse aggregate may be reduced while on the other hand

corresponding increases may be made in that of the finer aggregates.

(iii) The process of mixing concrete can be repeated second time by use of the vibrator.

(iv) Proportionate increases may be made in the quantity of water and cement as well such that the water cement ratio is maintained.

Water cement ratio

Water cement ratio is the ratio of the water in a mix (excluding water absorbed already by the aggregate) to the weight of cement their in. ‘water cement ratio’ is the most important factor governing the strength of concrete. The strength of the concrete depend mainly open the amount of cement and the amount of water in it. The correct quantity Of water cement ratio required for a particular mix depends upon various factors such as mix proportions, type and grading of aggregate, method of compaction applied and weather condition.

On the other hand workability of a concrete mix increases as the water content or water cement ratio of mix increased, because the water lubricate the mixture. But, at the same time increases in water content deceases the strength. Excess of water, further weaken the concrete, produces shrinkage cracks and decreases density.

Manufacture of the concrete

In the manufacture of concrete, it is almost important to ensure that a concrete of predetermined proportion is continuously placed in position in such a way that each batch almost like the other batches as far as possible.

Batching of the concreteAfter fixing the proportion of different ingredients of concrete for a particular work, the material C.A., F.A., cement and water measured out in batches for mixing. The process is known as Batching. This process of batching may be carried out by weight or by volume.

(i) Weight batching:- The unit of weight, for material of concrete, is usually Kilogram. The batching of material by weight is absolutely straightforward, the cement, sand and coarse aggregate being all weighed directly in Kilogram.

(ii) Volume batching:- In batching by volume, all ingredient i.e. water, cement, sand and coarse aggregate are measured in liters, where the resulting concrete (being) solid measured in cubic meters.

Mixing of concreteMixing of concrete may be carried out by hand or machine (by using a mechanical mixture) but the mixing by machine is always preferred.

(i) Mixing by hand:- In this, mixing carried out by hand on a clean, hard and water tight platform. Firstly cement, sand, aggregate are mixed by hand with the help of the shovel and a desired quantity of the water added to it and mix properly. This type of mixing carried out in the small work and unimportant work.

(ii) Mixing in machine: - The machine used

for mixing concrete is known as mechanical concrete mixer. There are two main type of concrete mixer is commonly use namely:

Continuous mixers are used in massive construction such as dams, bridges, etc., which involve the use of large masses of concrete and also required the continuous flow of concrete.

Batch mixer is most commonly used and consisting of a revolving drum with blades or baffles inside it. In batch mixer, all the material of desired proportioned mix are fed into the hopper of the revolving drum on being rotated at a certain speed mixes the material with the aid of a series of blades providing inside, the resulting mix is finally discharged from the drum and conveyed for used.

Placing and finishing of concrete

Mixing, transporting, and handling of concrete should be carefully coordinated with placing and finishing operations. Concrete should not be deposited more rapidly than it can be spread, struck off, consolidation, and bull floated. Concrete should be deposited continuously as near as possible to its final position. In slab construction, placing should be started along the perimeter at one end of the work with each batch placed against previously dispatched concrete. Concrete should not be dumped in separate piles and then leveled and worked together; nor should the concrete be deposited in large piles and moved horizontally into final position.

Vibration either internal or external is the most widely used method for consolidating concrete. When concrete is vibrated, the internal friction between the aggregate particles is temporarily destroyed and the concrete behave like a liquid; it settles in the forms under the action of gravity and the large entrapped air voids rise more easily to the surface. Internal friction is reestablished as soon as vibration stops.

FinishingConcrete that will be visible, such as slab like

driveway, highway or patios often need finishing. Concrete slabs can be finished in many ways,

depending on the intended service use. Options include various colors and textures, such as exposed aggregate or a patterned stamped surface. Some surface may require only strike off and screeding to proper contour and elevation, while for other surface a broomed, floated, or troweled finish may be specified. In slab construction screeding or strike off is the process of cutting off excess concrete to bring the top surface of the slab to proper grade. A straight edge is moved across the concrete with a sawing motion and advanced forward a short distance with each movement.

Bull floating eliminates high and low spots and embeds large aggregate particles immediately after strike off.

Curing of concrete

Curing is one of the most important step in concrete construction, because proper curing greatly increase concrete strength and durability. Concrete hardened as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete temperature stayswithin a suitable range. During the curing period from five to seven days after placement for conventional concrete the concrete surface needs to be kept moist to permit the hydration process. New concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.

After concrete is placed, a satisfactory moisture contents and temperature (between 50º F and 75º F) must be maintained, process called curing. Adequate curing is vital to quality concrete. Curing has a strong influence on the properties of hardened concrete such as durability, strength, water tightness, abrasion resistance, volume stability and resistance to freezing and thawing and deicer salts. Exposed slab surfaces are especially sensitive to curing. Surface strength development can be reduced significantly when curing is defective.

Common tests on the fresh concrete

Concrete is tested to ensure that the material that was specified and bought is the same material delivered to the job site. There are a dozen different test methods for freshly mixed concrete and at least another dozen tests for hardened concrete, not including test method unique to organization like the Army Corps of Engineers, the Federal Highway Administration, and State department of transportation.

Slump, air content, unit weight and compressive strength tests are most common tests.

Slump is a measure of consistency, or relativeability of the concrete to flow. If the concrete can’t flow because the consistency or

slump is too low, there are potential problems with proper consolidation. If the concrete won’t stop flowing because the slump is too high, there are potential problems with mortar loss through the formwork, excessive formwork pressure, finishing delays and segregation.

Ø Air content measure the total air content in a sample of fresh concrete, but does not indicate what the final in-place air content will be, because a certain amount of air is lost in transportation Consolidating, placement and finishing. Three field tests are widely specified: the pressure meter and volumetric method are ASTM standards and the Chace Indicator is an AASHTO procedure.

Unit weight measures the weight of a knownvolume of the fresh concrete.

Ø Compressive strength is testes by pouring cubes of fresh concrete and measuring the force needed to break the concrete cubes at prescribed interval as they harden. According to Building Code Requirements for reinforced concrete (ACI 318) as long as no single test more than 500 psi below the design strength and the average of three consecutive tests equals or exceed the design strength then the concrete is acceptable. If the strength tests don’t meet these criteria, steps must be taken to raise the average.

INDEXBasic data for the Building:

A. (1). Thickness of the raft 0.70 m(2). Projection of raft beyond footing 0.50 m(3). Projection of raft beyond basement 0.50 m(4). Depth of sand filling on the raft 0.50 m(5). Thickness of P.C.C. below raft 0.075 m(6). Projection of P.C.C. beyond raft 0.075 m(7). Depth of lift pit 1.70 m

B. Floor Height(1). Top of pad to first basement level 4.00 m(2). Top of first basement to ground level 3.30 m(3). Ground floor to first floor 4.20 m(4). First to second & second to third floor 4.20 m(5). Third floor to roof 4.15 m

C. Depth of excavation(1). First lift 1.50 m

(2). Second lift 7.375 m